Field of the Invention
This invention relates to sensing the position of an object placed within a living body. More particularly, this invention relates to improvements in a catheter tracking system using impedance measurements.
Description of the Related Art
The meanings of certain acronyms and abbreviations used herein are given in Table 1.
TABLE 1Acronyms and AbbreviationsACLActive Current LocalizationEMElectromagneticMRIMagnetic Resonance Imaging
A wide range of medical procedures involve placing objects, such as sensors, tubes, catheters, dispensing devices, and implants, within the body. Real-time imaging methods are often used to assist doctors in visualizing the object and its surroundings during these procedures. In most situations, however, real-time three-dimensional imaging is not possible or desirable. Instead, systems for obtaining real-time spatial coordinates of the internal object are often utilized.
U.S. Pat. No. 7,756,576 to Levin, whose disclosure is herein incorporated by reference, describes determining in near real-time the position of a probe placed within a living body. Electric currents are driven between one or more electrodes on the probe and electrodes placed on the body surface. The impedance between the probe and each of the body surface electrodes is measured, and three-dimensional position coordinates of the probe are determined based on the impedance measurements. Dynamic compensation is provided for changing impedance of the body surface and its interface with the electrodes.
U.S. Patent Application Publications 2006/0173251, of Govari et al., and 2007/0038078, of Osadchy, which are herein incorporated by reference, describe impedance-based methods for sensing the position of a probe by passing electrical currents through the body between an electrode on the probe and a plurality of locations on a surface of the body.
Impedance-based tracking systems have often been combined with another tracking system, e.g., an imaging modality such as fluoroscopy or magnetic resonance imaging, which is applied to the region of catheter insertion.
In another approach, U.S. Patent Application 2007/0016007, of Govari et al., whose disclosure is incorporated herein by reference, describes a hybrid magnetic-based and impedance-based position sensing system.